Iraq’s Ministry of Religious Affairs said Sunday that Ayatollah Hussein Bahr Al Oulum died of a heart attack earlier this week, ruling out reports that he was assassinated under “mysterious circumstances."

"Ayatollah Hussein Bahr Al Oulum, more than 70 years old, died Friday from a heart attack," according to a ministry obituary carried by newspapers, quoted by AFP.

The ministry said the ayatollah, who was buried in the holy city of Najaf south of Baghdad the same day, "was known for his nationalist stands, especially during the Iran-Iraq war and the 'Mother of All Battles' (the 1991 Gulf War)."

But Al Oulum’s family on Saturday said he assassinated, reported the official Iranian news agency (IRNA).

In a communiqué issued from London, a copy of which was made available to IRNA, they said that the ayatollah had been killed in Iraq under "mysterious circumstances" early Friday.

Iran's students news agency ISNA had already cited Beirut-based newspapers as saying that unknown people had entered Ayatollah Bahr Al Oulum's house in the southern holy city of Najaf and had assassinated him "in a brutal manner." The cleric, his family said, had been refusing to cooperate with the “Iraqi Baathist regime” and was an active campaigner for the release of jailed Shiite clerics in the country.

He was also a regular critic of the Iraqi regime for its mistreatment of Shiite clerics, the family said in another part of the communiqué.

According to IRNA, the assassination of Ayatollah Bahr Al Oulum brings to four the number of top Shiite clerics killed in Iraq over the past four years. The assassins have never been identified.

According to Amnesty International's reports from the 1970s and 1980s, the Iraqi government systematically deported tens of thousands of Shiite people to Iran, claiming they were of Persian descent – Albawaba.com